1. Field of the Invention
The present invention relates generally to a steam turbine plant. More particularly, the present invention relates to a start-up method of the steam turbine plant wherein at the start-up of the steam turbine plant, a condensate supplied into a condenser is deaerated so as to allow the condensate to be supplied to a boiler within a short time.
Further, the present invention relates to a condenser serving to condense an exhaust steam from a steam turbine thereby produce a condensate wherein the condenser is preferably employable for practicing the foregoing start-up method of a steam turbine plant.
2. Description of the Related Art
In recent years, a combined cycle power plant has been highly evaluated as a power generating system which assures that two excellent properties, i.e., a facility of load change and a high thermal efficiency can be achieved. To raise up a level of the excellent properties as mentioned above further, research and development works have been conducted so as to improve a method of operating a power plant and apparatuses and instruments associated with the foregoing method. The latest remarkable activity with respect to the method of operating a power plant is a shift from a base load operation to a daily start and stop operation (hereinafter referred to simply as a DSS operation). Accordingly, research and development works have been conducted based on the DSS operation for the purpose of improving apparatuses and instruments associated with a steam turbine plant.
To facilitate understanding of the present invention, a typical conventional combined cycle power plant will briefly be described below with reference to FIG. 7.
As shown in FIG. 7, an air pressurized by a compressor 100 is supplied into a combustion chamber 102 in which the pressurized air is mixed with a fuel supplied via a fuel supply system (not shown) to generate a combustion gas having an elevated temperature. The combustion gas is then supplied into a gas turbine 104 as a working fluid for rotating the gas turbine 104. Since the combustion gas which has been expanded after the usage for the rotation of the gas turbine 104 has still a high temperature (about 550.degree. C.), it is delivered from the gas turbine 104 to a heat recovery steam generator (hereinafter referred to simply as HRSG) 106 in which it serves as a working fluid for a heat supply source available for a steam turbine system. Thereafter, the combustion gas is discharged to an atmosphere as an exhaust gas.
On the other hand, a feed water pressurized by a low pressure feed water pump 108 in the steam turbine system is first supplied into a low pressure economizer 110 in which the pressurized feed water is heated by the combustion gas from the gas turbine 104 flowing through the HRSG 106. Thereafter, the pressurized feed water is distributed to three systems, i.e., a lower pressure system, an intermediate pressure system and a high pressure system.
With respect to the low pressure system, the feed water is fed from a low pressure steam drum 112 to a low pressure evaporator 114 in which it is heated and evaporated as a steam. The resultant steam is superheated in a low pressure superheater 116 and the superheated steam is then supplied into a low pressure turbine 118.
With respect to the intermediate pressure system, the feed water is pressurized by an intermediate pressure feed water pump 120 and the pressurized feed water is then fed via an intermediate pressure economizer 122 and an intermediate pressure steam drum 124 to an intermediate pressure evaporator 126 in which the pressurized feed water is heated and evaporated as a steam. The steam is superheated in an intermediate superheater 128 and the superheated steam is then supplied into an intermediate pressure turbine 130.
With respect to the high pressure system, the feed water is pressurized by a high pressure feed pump 132 and the pressurized steam is then fed via a high pressure steam drum 136 to a high pressure evaporator 138 in which it is heated and evaporated as a steam. The steam is superheated in a high pressure superheater 140 and the superheated steam is then supplied into a high pressure turbine 142.
As is apparent from the drawing, the low pressure turbine 118, the intermediate pressure turbine 130, the high pressure turbine 142 and the gas turbine 104 are connected directly to a generator 144 in which an electric power is generated, respectively.
Further, exhaust steams from the low pressure turbine 118, the intermediate turbine 130 and the high pressure turbine 142 are delivered to a condenser 146 in which the exhaust steams are condensed by a cooling water flowing through a number of condenser tubes constituting a tube bundle 148. Water falls down on a hot well 150 in the condenser 146 in which it is received and stored as a condensate. Thereafter, the condensate is extracted from the hot well 150 by a condensate pump 152 and then delivered to the low pressure feed water pump 108 via a gland steam condenser 154.
Steams leaked from glands of the respective turbines (i.e., the low pressure turbine 118, the intermediate pressure turbine 130 and the high pressure turbine 142) are collected via a gland steam pipe 156 in the gland steam condenser 154 in which the leaked steams are condensed by condensate and thereby a thermal energy of the leaked steam is recovered.
In addition, the condenser 146 is provided with a venting equipment 158 for extracting a non-condensibles and associated water vapor to produce the minimum steam condensing pressure.
To lower a dissolved oxygen concentration of the condensate during operation of the steam turbine plant, a part of the condensate is returned via a condensate recirculating system 160 to the condenser 146 in which it is subjected to deaeration while it is heated by the exhaust steam from the steam turbine system.
In FIG. 7, reference numeral 162 designates a makeup water pipe through which a makeup water is additionally supplied to the condenser 146 to compensate for shortage of a condensate when a quantity of the condensate stored in the condenser 146 is excessively reduced, reference numeral 164 designates a stop valve disposed on the condensate recirculating system 160, reference numeral 168 designates a stop valve disposed on the inlet side of the condensate pump 152 and reference numeral 170 designates a stop valve disposed on the inlet side of the venting equipment 158.
With the steam turbine plant as constructed in the above-described manner, when a dissolved oxygen concentration of the condensate is elevated, there arises a certain malfunction. For example, the pipes in the HRSG 106 are corroded intensely. To avoid an occurrence of the malfunction as mentioned above, it has been required that the dissolved oxygen concentration is maintained within the range lower than 80 ppb at the time when operation of the steam turbine plant is to be started.
During the shut-down of the steam turbine plant, a large quantity of condensate is stored in the hot well 150 in the condenser 146 in preparation of next start-up operation of the steam turbine plant. However, since an atmospheric air is unavoidably penetrated into the interior of the condenser 146 during the shut-down of the steam turbine plant, a long period of waiting time elapses until operation of the steam turbine plant is started, as the condensate is brought in contact with the atmospheric air. For this reason, a large quantity of oxygen is dissolved in the condensate with the result that the dissolved oxygen concentration varies to a very high value in excess of a preset value of 7 ppb which should be maintained during operation of the steam turbine plant. For example, provided that no measure is taken not only to prevent an atmospheric air from penetrating the condenser 146 but also to prevent an oxygen in the atmospheric air from being dissolved in the condensate, a value of the dissolved oxygen concentration is raised up to a high value of 10000 ppb.
Provided that the dissolved oxygen concentration which has been raised up to a level of 10000 ppb should be lowered to 80 ppb with the aid of the condensate recirculating system 160, there is required a long time to deaerate the condensate. Thus, there is a possibility that a time consumed for deaerating at every time of DSS operation is elongated and the steam turbine plant fails to quickly meet the requirement from the electricity consumers' side.